Fact checking Ashby

[Beendare]

Have you ever shot an arrow that’s 1000+ grains? Built some for Neil Summers for an elephant hunt. He shot them out of a Mathews Monster. There was actual felt recoil from the bow trying to push that heavy of an arrow. Crazy stuff.

Almost, 840g for Australian buff

 

[Mighty Mouse]

I love a good technical clarification and I agree that Ashby and the ABF guys aren't the most technically sound on physics, but ChemProfJSpencer's videos on mechanical advantage all boil down to simply affirming Ashby's claim that (all else equal) higher MA improves penetration.

From 4:43 in the video below (emphasis mine):

"So this one [the 3:1 broadhead] basically reduces the force acting directly against the edge to 16-17% of the total force acting on the broadhead, on the arrow. This one, the shorter stubbier Iron Will, reduces that to only 42% of the total force value. So in other words, for the Iron Will, the edge experiences significantly more forces acting on it as it penetrates an animal than the edge does for a 3:1 broadhead. This sort of supports my idea that the shorter, stubbier broadhead is going to need better metal to resist this stronger force acting directly on the edge trying to roll the edge, dull it, chip it. And the 3:1 broadhead’s going to get away with a lot less force acting on each portion of the edge."​

​

The edge forces he's referring to are also working to slow the arrow down and stop penetration (in addition to trying to deform the edge). Reducing those edge forces will increase penetration. The key challenge in trying to quantify the penetration difference attributable to MA is that rarely (if ever) are all other factors equal between two differently shaped broadheads (e.g., blade thickness, bevel angle, edge sharpness/hardness, ferrule shape, etc). I would contend that Ashby is directionally correct in his claims about MA but likely overstates the magnitude of the effect.

 

[Billy Goat]

Ok gotcha.
There was a website that did some testing on this back in the day, Archery Report or something like that.…Im not sure its still around but it was good stuff.

The real question is at what point does KE fall off? As I recall the KE and momentum fall off around 1800grains but I cant remember the exact number. Its surprisingly high. Its the reason why guys shoot 1200g arrows for elephants and hippos.

.

I'm kinda surprised it's that low honestly, but of course it changes with draw length and poundage.

I can remember seeing KE fall off before when playing with heavy arrows from lighter draw weight bows, but that could have been from inaccuracies in Chrono readings as well. I think I was playing with shafts up to 800 grains out of a 29" 60# bow. KE will fall off before momentum, it weighs heavy on velocity. Momentum puts everything in the mass, I don't think either are perfect for deciding what to use with a setup, however they do offer a comparison between different setups.

They are both just a fraction of the total setup. Many things need to be considered, just depends on the environment they are being used in.

 

[Billy Goat]

Have you ever shot an arrow that’s 1000+ grains? Built some for Neil Summers for an elephant hunt. He shot them out of a Mathews Monster. There was actual felt recoil from the bow trying to push that heavy of an arrow. Crazy stuff.

I built some shafts in 2010 that were 960gr. I was using them in an 84# Hoyt Katera.
It could shoot thru 1/8" steel under 35 yards with the right bullet point. The recoil was pretty cool.

 

[4fletch]

I'm kinda surprised it's that low honestly, but of course it changes with draw length and poundage.

I can remember seeing KE fall off before when playing with heavy arrows from lighter draw weight bows, but that could have been from inaccuracies in Chrono readings as well. I think I was playing with shafts up to 800 grains out of a 29" 60# bow. KE will fall off before momentum, it weighs heavy on velocity. Momentum puts everything in the mass, I don't think either are perfect for deciding what to use with a setup, however they do offer a comparison between different setups.

They are both just a fraction of the total setup. Many things need to be considered, just depends on the environment they are being used in.

KE is an all but worthless metric when it comes to arrows. At least with momentum you have a solid starting point. Two arrows with the same momentum will have close to the same potential on target, two arrows with the same KE could be so wildly different that one could fail to pen a lethal distance and the other could be a pass through, repeatedly.

 

[robby denning]

There is a professor peer reviewing the Ashby stuff over on AT and -Spoiler alert- if you drank the Ashby and Ranch Fairy Koolaid… you are going to be dissapointed in your idols.

On AT you can search the posts by Ugly Joe- his nickname over there.
He posted a couple of videos on Youtube, this one points out how Ashby misapplied the Physics on his studies on Mechanical Advantage. This vid is short and sweet.
His vid captures why a 2 blade is so effective as a penetrator ……and why the short wide 3, 4 blades have more resistance.

its titled, “ The myth of mechanical advantage and the 3:1 ratio” by ChemprofJSpencer

HERE
His additional commentary on AT backs what we have known for centuries; heavier arrows are a big factor in arrow penetration…much more than FOC. It seems Ashby putting it at #3 is wishful thinking.

He also has a 45 minute vid that goes through FOC. Its long and math heavy, He analyses the compressive portion of the launch, something no one else addresses- he captures arrow forces though he uses arrow mass as a constant. ( in the real world, its not) The conclusion is there is advantages to some foc.

We all know more tip weight needs more arrow spine…and his followup comment to that on AT is that this added arrow mass can account for much of the additional penetration advantage Ashby attributes to FOC.

The bottom line on all of this and all of the experienced guys will be saying; DUH!

We need an arrow that can reasonably handle whatever tip weight ( who knew that the Easton engineers were right all along?) ….so it won’t be a surprise to the experienced bowhunters that massive FOC is a destabilizing force on the launch. Easton was right, FOC somewhere in the teens or there abouts is about the perfect equation for stabile arrow flight and good arrow performance.

Professor JSpencer said this was all prompted by the Asby foundation article in Dallas Safari club, “ That is so wrong” where they misapplied the physics in their recommendations.
.
Its all vindication for what the many of the experienced guys have been saying for years….including myself.

.

Thanks for posting this up. Reminds me of what one of my professors taught me, “math don’t lie“


Sent from my iPhone using Tapatalk

 

[wapitibob]

Guys spending weeks and months trying to build an arrow to compensate for their shitty shots would be way ahead if they just spent that time on the range.

 

[Beendare]

Mighty,
its worth reading his commentaryover on AT.

The professor is not sayin MA doesn’t matter…in fact he states it absolutely does.

What he is saying is Ashby’s claim of 3:1 taper ratio is misapplied. A 2 blade BH has massive MA….due to the thin cross section.

Intuitively we have all seen this And we jnow that a 3;1 BH is going to be the same as a 2;1 BH in performance on game.

Personally, I think there is a point where that ratio matters. A BH with too shallow an angle will be putting more blade edge against hair and hide…vs a head with more taper slicing in and avoiding all that. I dont know what that cutoff point is.

Ive used 3;1 heads and they are very weak out on the tip, not good. I use a cheap 2.25;1 or so head and they work great.

I’m wondering:
Ive been told by my dad - who I suppose I can blame for my fascination in archery physics- that back to the 50’s this whole 3;1 ratio was a big discussion and there were others that studied it, even books on it ( a guy named Hancock I think) long before Ashby. Thats the origination of all this 3;1 stuff, how it became Ashby’s- who knows.


.

 

[Beendare]

I'm kinda surprised it's that low honestly, but of course it changes with draw length and poundage.

I can remember seeing KE fall off before when playing with heavy arrows from lighter draw weight bows, but that could have been from inaccuracies in Chrono readings as well. I

Yeah, Probably inaccuracies. A heavier starting mass- heavier arrow- absorbs more of the bows energy. This is why KE continues to rise with the heavier arrow. When we go a little heavier arrow wise, our bow is quieter. The noise in the bow is excess energy that a lighter arrow doesn’t absorb From the bow and that energy is exhibited by extra noise and vibration in the bow.

Now whether KE or momentum is is the best formula has been debated for years.

Guys use these formulas to evaluate The difference between hunting arrows, right?
Its much easier than doing those calcs; if you want more penetration out of your arrow all else equal, just bump up the weight. It really is that easy!

 

[Beendare]

Thanks for posting this up. Reminds me of what one of my professors taught me, “math don’t lie“


Sent from my iPhone using Tapatalk

Yeah no problem.

And as is typical of these influencers, there are some truths mixed in with the not so true stuff to make it seem more legit.

Example; Average arrow weight is good… so if thats good, then massive arrow weight must be BETTER, right?

They use the same extrapolation on FOC.

Common sense tells us there’s a point of diminishing returns.

Then again I use the same strategy persuading my wife; some hunting gear is good but a lot of hunting gear is so much better!

.

 

[Read1t48]

This is a great thread. I’m going over to AT for the read. I’ve been having this exact discussion with friends. The Prof. is in my corner.
I do like the fact that Ashby and the RF help create good discussions. A great bow hunter should prove their theories firsthand. Unfortunately, we live in a society where shortcuts are the norm. Just give me the solution! That doesn’t work out well for all the variables associated with each individual archer and their equipment.

 

[Mighty Mouse]

Mighty,
its worth reading his commentaryover on AT.

I generally avoid AT, but I'll make an exception and have a look. Post a link to the AT thread if you've got it, please.

The professor is not sayin MA doesn’t matter…in fact he states it absolutely does.

What he is saying is Ashby’s claim of 3:1 taper ratio is misapplied. A 2 blade BH has massive MA….due to the thin cross section.

I get his point about the wedging effect/material displacement acting perpendicular to the plane of the head, not parallel to the blade edge. And I do agree that Ashby's explanations of MA aren't entirely accurate. But the length-width ratio (perhaps that's a less objectionable term than MA) of a head does affect the resistance the head encounters when traveling though an animal, which in turn affects its ability to penetrate. In the video I quoted above, ChemProf explains how the resistance forces acting on the blade edge decrease with increasing length-width ratio, he just chooses to focus on the implications for edge material/strength instead of on overall penetration.

Personally, I think there is a point where that ratio matters. A BH with too shallow an angle will be putting more blade edge against hair and hide…vs a head with more taper slicing in and avoiding all that. I dont know what that cutoff point is.

Agreed. I think the benefit of a head with more taper/greater length-width ratio will be most pronounced on entry. The hide will deflect to some degree before the initial cut forms, and I expect a short/shallow head will allow more deflection and lose more momentum while cutting the initial hole than a long/steeply-tapered head.

Ive used 3;1 heads and they are very weak out on the tip, not good. I use a cheap 2.25;1 or so head and they work great.

I’m wondering:
Ive been told by my dad - who I suppose I can blame for my fascination in archery physics- that back to the 50’s this whole 3;1 ratio was a big discussion and there were others that studied it, even books on it ( a guy named Hancock I think) long before Ashby. Thats the origination of all this 3;1 stuff, how it became Ashby’s- who knows.

Everything is a tradeoff. As length-width ratio increases, ability to penetrate improves but the tip becomes more prone to bending/breaking. I don't think there's anything magical about a 3:1 ratio; those that claim there is are just regurgitating another one of Ashby's misguided attempts to establish definitive "threshold" values for various aspects of arrows. Better combinations of penetration and strength may well exist at ratios less than 3:1.

 

[Foggy Mountain]

What amazes me is it’s all irrelevant to most in North America even if the info was correct. Not one compound of any decent weight won’t blow through deer even if things are way “off” . A buddy of mine shoots 70lbs and is quoting ridiculous stuff when he’s shot a pile with relatively inefficient gear like mechanical heads and super light arrows. It’s a bill of goods boys

 

[4fletch]

Now whether KE or momentum is is the best formula has been debated for years.

Guys use these formulas to evaluate The difference between hunting arrows, right?
Its much easier than doing those calcs; if you want more penetration out of your arrow all else equal, just bump up the weight. It really is that easy!

The issue being the same bow shoots a 350g arrow 340 fps and a 500g arrow 280fps. Thats .527 m and 89.75ke for the light and fast and .621m and 86.95ke for the heavy slower.
The problem being if you use KE as a metric for killing with a bow it will fail you. Its an energy transfer data point if you will. And arrows do not do that outside flat points on bird and small game. Using KE you would think the 350g arrow would be remarkably better on game. Using KE as a kill metric for what setups are enough people would think a 350g arrow moving 340fps is better for heavy game and a 500g arrow going 280fps isnt enough.
KE is a good metric for firearms that transfer energy to the target. Arrows "just" overcome resistance. From the string and through animal that is what they do. Momentum is the best starting point to figure how much resistance they can overcome.

 

[Reburn]

KE is a good metric for firearms that transfer energy to the target.

Sorry bud your wrong here, KE has nothing to do with killing power in firearms either. There is hundred of pages of threads on this. Minimum velocity required for expansion and bullet construction are more pertinent for wheter or not a bullet will perform. Energy transfer into a target doesnt kill, bullet expansion and fragmentation does as it creates Destroyed lungs and vitals. KE means nothing. Refrence 223 for elk bear and moose thread in the firearms section for a light read.

 

[4fletch]

Sorry bud your wrong here, KE has nothing to do with killing power in firearms either. There is hundred of pages of threads on this. Minimum velocity required for expansion and bullet construction are more pertinent for wheter or not a bullet will perform. Energy transfer into a target doesnt kill, bullet expansion and fragmentation does as it creates Destroyed lungs and vitals. KE means nothing. Refrence 223 for elk bear and moose thread in the firearms section for a light read.

Bullets faster than the average handgun create primary, secondary and tertiary wounding. I recommend YOU look at some battlefield pictures of damage done by the 5.56 vs the slower bigger rounds on the human body. Or better yet look at pistol bullets of the same weight as say the 270 winchester on game. Rifle bullets transfer energy, They open tissue, tear and bruise, cause damage and disrupt organ function. Meanwhile when you remove velocity but still have a bullet that expands you remove all that and are just "poking holes". This is why Elmer Keith spent so much time creating magnum handgun rounds. This is why full load 10mm and 44mag are the chosen sidearm in Alaska and not .40. To the point if you were correct .40 and 10mm would have the same effect on game, and it has been shown repeatedly they do not.

 

[Reburn]

Bullets faster than the average handgun create primary, secondary and tertiary wounding. I recommend YOU look at some battlefield pictures of damage done by the 5.56 vs the slower bigger rounds on the human body. Or better yet look at pistol bullets of the same weight as say the 270 winchester on game. Rifle bullets transfer energy, They open tissue, tear and bruise, cause damage and disrupt organ function. Meanwhile when you remove velocity but still have a bullet that expands you remove all that and are just "poking holes". This is why Elmer Keith spent so much time creating magnum handgun rounds. This is why full load 10mm and 44mag are the chosen sidearm in Alaska and not .40. To the point if you were correct .40 and 10mm would have the same effect on game, and it has been shown repeatedly they do not.

Great. I love rehashing these converstation with new guys.

Handguns isnt what we were talking and we arent going there as thats a whole other bag of worms. We arent discussing anything that is in a transonic or subsonic window with guns.

Velocity causes expansion and fragmentation of bullets. There are many papers out there on the wounding mechanisim of bullets and hydrostatic shock is the least proven and least agreed upon mechanism of wounding.

Secondly the temporay stretch cavity is not determined by KE OR bullet diameter but rather bullet construction and rate of expansion. Thats what makes the sierra TMK such a magical killer of a bullet even at 77 grains out of a 223 which is neither a fast or a heavy bullet so it doesnt have fantasitc KE numbers.

Lets put this conversation back on track. There are plenty other guys that would love to hear your expertise and thoughts on guns bullets an wounding on this other thread. See you there.

.223 for bear, deer, elk and moose.

DON'T HAVE TIME TO READ 176 PAGES? HERE'S THE CHEAT SHEET. “Bullets matter more than headstamps.” “Spent primers offer the supreme tutorial”. I’ve read it here and elsewhere online. It got my attention. I started digging and asking questions and listened. The 77gr TMK delivered by a .223...

www.rokslide.com

 

[4fletch]

Great. I love rehashing these converstation with new guys.

Handguns isnt what we were talking and we arent going there as thats a whole other bag of worms. We arent discussing anything that is in a transonic or subsonic window with guns.

Velocity causes expansion and fragmentation of bullets. There are many papers out there on the wounding mechanisim of bullets and hydrostatic shock is the least proven and least agreed upon mechanism of wounding.

Secondly the temporay stretch cavity is not determined by KE OR bullet diameter but rather bullet construction and rate of expansion. Thats what makes the sierra TMK such a magical killer of a bullet even at 77 grains out of a 223 which is neither a fast or a heavy bullet so it doesnt have fantasitc KE numbers.

Lets put this conversation back on track. There are plenty other guys that would love to hear your expertise and thoughts on guns bullets an wounding on this other thread. See you there.

.223 for bear, deer, elk and moose.

DON'T HAVE TIME TO READ 176 PAGES? HERE'S THE CHEAT SHEET. “Bullets matter more than headstamps.” “Spent primers offer the supreme tutorial”. I’ve read it here and elsewhere online. It got my attention. I started digging and asking questions and listened. The 77gr TMK delivered by a .223...

www.rokslide.com

LOL, "do not use any examples that show velocity in fact is a determining factor in effect on target"
I do not do running goal post conversations.
Hint hint, tmjs cause cavitation, showing your claim incorrect. As a matter of fact Bohning showed an arrow doing it in ballistics gel.
Death is caused by blood loss, cutting off the ability to breath or damage to the cns in the end. However massive damage to the body or organs has another effect of shutting the body down. I have seen guys unload on Moose and they just lay down and slowly die. I have also seen them seize up and flop over with roughly the same shot placement and bullet weight/diameter just a whole lot faster.
Sorry pal but from Taylor to Keith and on to Jack O and Roy Weatherby its been shown hands down, Speed kills. (with firearms)Anything the 06 can do the 300WM can do better. If you were correct the 308 and the 300wm would have the same effect on game. The 7mm 08 and the 7mmRm would have the same effect on game. You are demonstrably wrong.

 

[Wrench]

I love these threads... if you are moved by what anyone else says to the point of changing your system/plan/form/components.... etc,

You probably need to spend more time killing shit and taking it apart and less time reading about parts.

Make your arrow fly like a drill bit, smash it into the target hitting as small or few bones as possible, keep as sharp/tough as possible and tough enough not to deform.....and go pick up your dead stuff and eat it.

 

[Reburn]

LOL, "do not use any examples that show velocity in fact is a determining factor in effect on target"
I do not do running goal post conversations.
Hint hint, tmjs cause cavitation, showing your claim incorrect. As a matter of fact Bohning showed an arrow doing it in ballistics gel.
Death is caused by blood loss, cutting off the ability to breath or damage to the cns in the end. However massive damage to the body or organs has another effect of shutting the body down. I have seen guys unload on Moose and they just lay down and slowly die. I have also seen them seize up and flop over with roughly the same shot placement and bullet weight/diameter just a whole lot faster.
Sorry pal but from Taylor to Keith and on to Jack O and Roy Weatherby its been shown hands down, Speed kills. (with firearms)Anything the 06 can do the 300WM can do better. If you were correct the 308 and the 300wm would have the same effect on game. The 7mm 08 and the 7mmRm would have the same effect on game. You are demonstrably wrong.

Ill reply to this as I can actually make this relevant to this thread.

jack and roy were a quite different time with different bullets. At their time with the componets they had avaliable they were correct. Comparing yesteryears bullets to todays bullets is asinine.

anything the 06 or 308 can do the 300wm can do better you claim.

Does the 300wm make the deer deader inside of the minimum expansion velocity for both rounds? Is the terminal wounding better with increased velocity on the same bullet?

Does the increased velocity of the WM at 300 yards make the deer deader? Does it make the bullet expand better?

How does comparing a 40 cal handgun at subsonic / transsonic speed with a completely different bullet construction have and relevance to a 270 at supersonic speeds with a different bullet construction.

Hint hint. The answer is no. The only thing the 300 wm does is increase the range at which you hit minimum expansion velocity.

Hint Hint. it has been proven that over 20 ft lbs of recoil and the accuaracy of a shooter decreases due to the increased recoil. Im sure your a stud and can shoot ultra mags 1/2 moa all day long without a flinch.

Hint Hint. Bad shot placement with a heavier bullet or arrow isnt going to make up for bad shot placement.